The present invention relates to an endoscope apparatus for observing a body cavity of a patient.
An insertion section of an endoscope is inserted in a body cavity of a patient to observe a portion to be examined.
In a conventional endoscope apparatus, the insertion section is constituted by a bundle of optical fibers. Such an insertion section is inserted in the body cavity to observe an image of the portion to be examined. At the same time, the image is photographed by, for example, a color video camera. The image is thus converted to a color video signal and the video signal is monitored or recorded. In addition, the color video signal can be converted to a digital video signal which can be stored in a memory. In this case, the image can be frozen at any time and a still image is displayed. This frozen or still image can then be photographed by a still camera.
Color solid-state image-pickup devices using a CCD (charge-coupled device), a MOS (metal oxide semiconductor) image sensor, an SIT (static induction transistor), or the like have been developed and used in recent years. This development work has resulted in the introduction of an endoscope apparatus having such a color solid-state image-pickup device mounted at the distal end of the insertion section. A video signal obtained by the solid-state image pickup device is sent through a conductive cable. In this apparatus, the insertion section mainly comprises the conductive cable, the solid-state image-pickup device, and a light guide consisting of the bundle of optical fibers for guiding light from a light source, to illuminate the body cavity. The video signal obtained by the solid-state image-pickup device is used for display and/or recording. In addition, the video signal can be converted to a digital signal which can be stored in a memory, so that the frozen image of the video signal can be displayed and can be photographed.
In a conventional endoscope apparatus of this type, a frozen image corresponds to a frame in a color video signal having a plurality of continuous frames. Therefore, the image information produced as a still image has a low S/N ratio. This low S/N ratio occurs for the following reasons: First, a noise component in a still image is more noticeable than that in a moving image. Second, since the color video signal has a wide frequency band, noise tends to be mixed therewith, and the video signal is then influenced by the noise component. Third, since the portion to be examined is observed through a pinhole aperture, so as to obtain a large depth of field, the amount of light reaching the detection surface, as the photographing portion of the video camera, is small, and the level of the resultant video signal is low.
The frozen image, therefore, has a low S/N ratio and cannot be easily exposed on a film, as a clear image. At present, as a matter of fact, the photographed film is observed by a plurality of doctors at different times and some doctors may miss important diagnostic data because of the poor quality of the image.